1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member and a method of producing the electrophotographic photosensitive member, and a process cartridge and an electrophotographic apparatus each including the electrophotographic photosensitive member.
2. Description of the Related Art
An electrophotographic photosensitive member containing an organic photoconductive substance (charge generation substance) is known as an electrophotographic photosensitive member to be mounted onto a process cartridge or an electrophotographic apparatus. The electrophotographic photosensitive member generally includes a support and a photosensitive layer (charge generation layer and hole transport layer) formed on the support. In addition, an intermediate layer has been formed between the support and the photosensitive layer for the purpose of suppressing injection of charge from the support to the photosensitive layer to suppress occurrence of an image defect such as fogging. Japanese Patent Application Laid-Open No. 2006-268011 discloses a technology involving incorporating metal oxide particles having small particle diameters into the intermediate layer to suppress the injection of the charge.
In addition, a charge generation substance having an additionally high sensitivity characteristic has been used in recent years. However, as the sensitivity of the charge generation substance rises, an amount of charge to be generated increases and hence the charge is liable to remain in the intermediate layer in an exposed portion. In addition, when image formation is repeatedly performed for a long time period, a voltage fluctuation is liable to become large. Japanese Patent Application Laid-Open No. 2008-250082 and Japanese Patent Application Laid-Open No. 2008-299344 each disclose, as a technology for suppressing such remaining of the charge of the intermediate layer, a technology involving using a laminated structure formed of a layer containing tin oxide-coated titanium oxide and a layer containing an electron transport substance for the intermediate layer to alleviate the voltage fluctuation. Japanese Patent Translation Publication No. 2009-505156 discloses a technology involving using a layer containing a polymer-type electron transport substance on a layer containing metal oxide particles to alleviate the voltage fluctuation.
However, studies made by the inventors of the present invention have found that when an intermediate layer obtained by laminating an intermediate layer containing metal oxide particles having small particle diameters and an intermediate layer containing an electron transport substance is used as the intermediate layer as described above, such a problem as described below arises. That is, the studies have found that the intermediate layer is susceptible to improvement because sufficient suppressing effects may not be obtained on a voltage fluctuation in an exposed portion and occurrence of a black spot under a high-temperature and high-humidity environment.